(a) Field of the Invention
The present invention concerns a device and a process for controlling the pressure of a gas which is fed to a user station through a gas supply line originating from a source of gas.
(b) Description of Prior Art
The known devices of this type conventionally utilize a control valve which is placed in the gas supply line, a pressure pick-up connected to a point of the line downstream of the valve, and a control logic operating valve. In order to control the pressure in a volume with a continuous flow or with zero flow, the pressure pick-up may be mounted in the immediate vicinity of the user station. This enables the control to be carried out with precision and without problem. However, there are systems for supplying gas where, for example under conditions of overcrowding or interchangeability of the downstream elements of the system, the pick-up may not be physically mounted in the vicinity of the user station, but substantially upstream of the latter, so that the load losses between the pick-up and the user station then become substantial. Under such conditions, in the case of a control with a continuous flow, the control will give a pressure which is systematically too low at the user station and, in the case of a rapid control with a flow of material which is weak or void, first there will be a cut-off of the control valve when the predetermined pressure is reached, followed by a reopening when the pressures are balanced. One may consider an electronic correction of the pressure signal given by the pick-up to try to restore the expected predetermined values at the user station. However, this correction is extremely delicate to obtain since it depends on the instantaneous flow which is variable and in general is difficult to measure.